This invention relates to a high-strength, high corrosion-resistant and non-magnetic stainless steel, particularly to a high Mn and high N high-strength, high corrosion-resistant and non-magnetic stainless steel.
Up to now, austenitic stainless steels such as Ni-containing SUS 304 (contains 0.08% or less of C, 1.00% or less of Si, 2.00% or less of Mn, 0.045% or less of P, 0.030% or less of S, 8.00 to 10.50% of Ni and 18.00 to 20.00% of Cr, and the remainder of Fe and inevitable impurities) and SUS 316 (contains 0.08% or less of C, 1.00% or less of Si, 2.00% or less of Mn, 0.045% or less of P, 0.030% or less of S, 10.00 to 14.00% of Ni, 16.00 to 18.00% of Cr and 2.00 to 3.00% of Mo, and the remainder of Fe and inevitable impurities) have been frequently used as materials for ornaments including necklaces, pierces and rings and for watchcases and watchbands.
Also, a Ni-containing austenitic stainless steel such as the SUS 316 or an SUS 316L (contains 0.03% or less of C, 1.00% or less of Si, 2.00% or less of Mn, 0.045% or less of P, 0.030% or less of S, 12.00 to 15.00% of Ni, 16.00 to 18.00% of Cr and 2.00 to 3.00% of Mo, and the remainder of Fe and inevitable impurities) has been frequently used in parts to be used in the living body, including dental materials and implant materials.
However, a problem is becoming serious mainly in Europe that these Ni-containing materials cause allergy due to Ni released into the living body.
In order to solve this problem, a so-called Ni-free stainless steel which does not contain Ni has been developed and its practical use is being attempted in Europe, by substituting Mn and N for Ni by pressurized ESR method.
However, though this Ni-free stainless steel has a high pitting resistance equivalent (Cr+3.3 Mo+16 N) which is frequently used as an index for corrosion resistance, it has a disadvantage in that its corrosion resistance is inferior to a Ni-containing stainless steel having the same equivalent.
Also, a low Ni stainless steel for biomaterial, which comprises 0.06% or less of C, 1.0% or less of Si, 15.0 to 22.0% of Mn, 0.030% or less of P, 0.015% or less of S, 1.0% or less of Ni, 15.0 to 18.0% of Cr, 0.5 to 4.0% of Mo, 0. 35 to 0.60% of N and 0.020% or less of 0, and further comprises, if required, one or two or more of 0.1 to 1.5% of Cu, 0.1 to 0.8% of W, 0.01 to 0.25% for each of Nb, V, Ti, Ta and Hf, Ca, Mg, B and REM as 0.0005 to 0.010% of Ca, 0.0005 to 0.010% of Mg, 0.0005 to 0.010% of B and 0.0005 to 0.010% of REM and 0.005 to 0.15% for each of Pt, Au, Ag and Pd, and the remainder of Fe and inevitable impurities, as an alloy which does not contain Ni, is described in Japanese Patent Application Laid-Open No. 10-121203.
However, though this alloy has no problem as a biomaterial use because of the low Ni, its corrosion resistance is not sufficient.
The object of the invention is to provide a high-strength, high corrosion-resistant and non-magnetic stainless steel which is further excellent in corrosion resistance and excellent for biomaterial body and also can stand against various corrosive environments.
In order to achieve this object, the present inventors have conducted intensive studies on a high-strength, high corrosion-resistant and non-magnetic stainless steel which does not contain Ni, is further excellent in corrosion resistance and biomateiral and also can stand against various corrosive environments, and found as a result that Mn contained in a large amount as a substitute element for Ni and to secure solubility of N deteriorates corrosion resistance and the corrosion resistance is improved by increasing the N content in a more larger amount by its pressurized melting and simultaneously decreasing the Mn content.
The invention has been accomplished based on these knowledge.
That is, according to the high-strength, high corrosion-resistant and non-magnetic stainless steel of the invention, it contains 0.15% or less of C, 1.0% or less of Si, 3.0 to 12.0% of Mn, 0.030% or less of P, 0.50% or less of Ni, 15.0 to 21.0% of Cr, 0.70 to 1.50% of N, 0.020% or less of Al and 0.020% or less of 0, and the rest substantially comprises Fe (the phrase xe2x80x9cthe rest substantially comprises Fexe2x80x9d as used in this specification means the remainder of Fe and inevitable impurities).
Also, according to the high-strength, high corrosion-resistant and non-magnetic stainless steel of the invention, it contains 0.15% or less of C, 1.0% or less of Si, 3.0 to 12.0% of Mn, 0.030% or less of P, 0.50% or less of Ni, 15.0 to 21.0% of Cr, 0.70 to 1.50% of N, 0.020% or less of Al and 0.020% or less of 0, and further contains one or two or more of 0.1 to 4.0% of Mo, 0.1 to 1.5% of Cu, 0.1 to 0.8% of W, 0.01 to 0.25% for each of Nb, V, Ti, Ta and Hf, 0.0005 to 0.0100% for each of Ca, Mg, B and REM, 0.03 to 0.4% of S, 0.005 to 0.05% of Te, 0.02 to 0.20% of Se and 0.0002 to 0.02% of Ca (excluding a case in which Ca is contained for the purpose of improving hot workability), and the rest substantially comprises Fe (i.e., the remainder of Fe and inevitable impurities).